Obesity is one of the worst enemies of human health. Obesity is an independent disease as well as a pathogenic cause of type II diabetes, cardiovascular diseases, hypertension, cerebral apoplexy and multiple cancers, is listed as one of top ten threats causing disease burdens by World Health Organization, and is a global issue that cannot be ignored. It is reported that about 18 million people die from cardiovascular and cerebrovascular diseases caused by diabetes and hypertension every year in the world, while the obesity is a key pathogenic factor of the diabetes and hypertension. The obesity seriously endangers human health and causes huge losses to the society. It is reported in 2003 that, expenditure for chronic diseases such as the obesity, the diabetes and the like reaches RMB 1200 billion in China and accounts for 10.3% of GDP. An increasing rate of the expenditure is higher than an increasing rate of Gross National Product (GNP). At present, domestic weight loss market needs are very wide. Consumption amount of weight loss products reaches RMB 60 billion in 2010, while losses caused by diseases, such as the diabetes, cardiovascular diseases and the like, directly or indirectly related to the obesity are beyond calculation. At present, although drugs for treating the obesity and the diabetes, i.e., fenofibrate and rosiglitazone, can achieve effects of reducing blood fat and blood sugar, serious side effects, such as insulin resistance, “mutagenesis, carcinogenesis and teratogenesis” effects and the like, may be caused to a human body when the drugs are taken for a long time. Therefore, safe, efficient and cheap novel drugs are urgently needed in clinical treatment of the obesity and the diabetes.
Leptin is a hormone substance secreted by adipose tissue. Six leptin receptors participate in fat metabolism and appetite regulation of the organism. At the beginning of this century, the leptin is discovered and successfully tested on a mouse model suffering from the obesity. A stir in scientific circles is created. It is forecast that biotechnology finds a novel weight loss drug for hundreds of millions of obese patients around the world. In 1999, through study, scientists have found out that polypeptide fragments of 116th-130th amino acid tissues of a human-derived leptin protein have obvious lipid degradation activities. Later, American scientists first carried out the first leptin protein experiment on human being. However, in 73 tested obese patients, most of the patients do not have an obvious weight loss effect, and only 2 patients lose weight by 35 pounds within 24 weeks, which indicates that an ideal weight loss effect is difficult to be achieved by using a wild type human-derived leptin protein.